1. Field of the Invention
This invention relates to an epitaxial substrate, a light-emitting diode, and methods for making the epitaxial substrate and the light-emitting diode, more particularly to an epitaxial substrate having light-transmissive members, a light-emitting diode having the epitaxial substrate, and methods for making the epitaxial substrate and the light emitting diode.
2. Description of the Related Art
Referring to FIG. 1, a conventional light-emitting diode (LED) includes an epitaxial substrate 11, a light-emitting unit 12, and an electrode unit 13. The epitaxial substrate 11 has a rough structure 111 formed thereon. The light-emitting unit 12 includes a first-type semiconductor layer 121 formed on the rough structure 111 of the epitaxial substrate 11, a light-emitting layer 122 formed on a portion of the first-type semiconductor layer 121, and a second-type semiconductor layer 123 formed on the light-emitting layer 122. The electrode unit 13 includes a first electrode 131 electrically connected to the first-type semiconductor layer 121, and a second electrode 132 electrically connected to the second-type semiconductor layer 123. When electricity is supplied to the light-emitting unit 12 through the first and second electrodes 131, 132, the light-emitting unit 12 will emit light by virtue of the photovoltaic effect. After the light from the light-emitting layer 122 travels to the rough structure 111 of the epitaxial substrate 11, it may be reflected or refracted so as to vary the travelling direction of the light to emit the light outwardly, thereby enhancing the light extraction efficiency of the LED.
In the conventional LED, the epitaxial substrate 11 and the rough structure 111 are made of the same material, and the rough structure 111 is usually made by roughening or patterning an upper surface of the epitaxial substrate 11 using an etching process. However, the epitaxial substrate 11 for the LED is commonly made of silicon, silicon carbide, aluminum oxide, etc., and is difficult to be etched. Accordingly, the etching process is time-consuming. Beside, the rough structure 111 may have poor dimensional accuracy, thereby resulting in uneven luminance of the LED.